[llvm] LAA: improve code in getStrideFromPointer (NFC) (PR #124780)

[David Sherwood via llvm-commits]

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@@ -2888,25 +2885,19 @@ static const SCEV *getStrideFromPointer(Value *Ptr, ScalarEvolution *SE, Loop *L
     return nullptr;
 
   V = S->getStepRecurrence(*SE);
-  if (!V)
-    return nullptr;
 
   // Strip off the size of access multiplication if we are still analyzing the
   // pointer.
   if (OrigPtr == Ptr) {
-    if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(V)) {
-      if (M->getOperand(0)->getSCEVType() != scConstant)
+    if (auto *M = dyn_cast<SCEVMulExpr>(V)) {
+      auto *StepConst = dyn_cast<SCEVConstant>(M->getOperand(0));
+      if (!StepConst)
         return nullptr;
 
-      const APInt &APStepVal = cast<SCEVConstant>(M->getOperand(0))->getAPInt();
-
-      // Huge step value - give up.
-      if (APStepVal.getBitWidth() > 64)
+      if (auto StepVal = StepConst->getAPInt().trySExtValue();
+          !StepVal || StepVal != 1)
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david-arm wrote:

`trySExtValue` returns std::optional<int64_t> so I don't know what `StepVal != 1` is actually testing here. I think you can just drop it.

https://github.com/llvm/llvm-project/pull/124780